The subject invention relates broadly to an apparatus for mixing high and low pressure air and more particularly but not by way of limitation, to a stepped area ratio ejector precooler for mounting between a jet engine and the air conditioning air duct of an aircraft for regulating a mixture of low pressure and high pressure air received from the jet engine.
Heretofore, a compressor section of a jet engine aircraft was used to supply energy in the form of pressurized air to the cabinet air conditioning system. This pressurized air is commonly called "bleed air" and is bled from bleed ports located at various stages of compression in a multi-stage compression section of the engine. To supply sufficient bleed air over the operating range of the aircraft, a high pressure bleed port is used. The temperature of this bleed air is normally too high for the cabin air conditioning system and some precooling of the bleed air is required. Cooling is usually accomplished through the use of a plate fin type heat exchanger. A cooler bleed air is bled from a low pressure bleed port of the engine compressor, passed through the heat exchanger and then discharged from the aircraft. Use of the high pressure bleed air from the cabin air conditioning plus the use of the low pressure bleed air for precooling penalizes the total operating condition of the engine in terms of fuel usage per unit propulsive thrust available to the aircraft. This penalty can be minimized if the air is extracted from a lower pressure stage of the engine and if discharging of the precooled bleed is eliminated. The subject invention embodies both these features.
Prior art aircraft cabin pressurizing systems are disclosed in U.S. Pat. No. 3,441,045 to Malone, U.S. Pat. No. 3,367,256 to Townsend et al, U.S. Pat. No. 3,367,255 to Terp, U.S. Pat. No. 3,842,720 to Herr, and U.S. Pat. No. 3,711,044 to Matulich. None of these environment control or pressurized systems disclose the unique features and advantages of the invention disclosed herein.